In the construction industry, structures can be coated with passive fireproofing material. Fireproofing material is known to provide fire resistance to substrates susceptible to fire, such as steel elements of buildings including beams, columns, roofs, decks, floors and plates and the like. These materials include spray applied fire resistant materials (SFRMs) which can be used for direct application to structural steel building members. They are predominantly cementitious or plaster-based. Their fire-resistive qualities and physical characteristics can vary widely between the respective types of SFRM. For example, the density of SFRMs are lower than normal weight concrete (e.g., 140-150+ lbs/ft3) and light weight (e.g., 90-150 lbs/ft3). Because SFRMs are made with ultra-light weight coarse aggregates, such as exfoliated vermiculite, mica, low density polystyrene etc., the materials are very porous. In-place density of the SFRMs is low (e.g., 15-60 lbs/ft3).
SFRMs can consist of inorganic binders such as plaster or Portland cement, and various fillers such as vermiculite, mica, limestone, gypsum, lightweight polystyrene beads, mineral wool, glass fibers, ceramic fibers, aluminum ore, clay and quartz. Examples of Portland-cement-based fireproofing products are Fendolite® MII from Isolatek International, Pyrocrete® 241 from Carboline and Monokote® Type Z-146 from W. R. Grace. Examples of plaster-based fireproofing products are Cafco® 300 from Isolatek International, Pyrolite® 15 from Carboline and Monokote® MK-6 from W. R. Grace.
Corrosion of SFRM coated substrates can be a concern. Typically, SFRMs comprise alkaline materials, such as Portland cement, which minimize the corrosion of the underlying substrate. Yet, when SFRMs are applied directly to the structural steel, aggressive agents, such as chloride ion (Cl−) or carbon dioxide (CO2) present in the surrounding medium can penetrate, cause protective oxides on metal substrates to breakdown and lead to the corrosion of the steel substrate.
Corrosion inhibitors have been widely applied in normal weight and lightweight concrete for corrosion protection of metals contained within the concrete. There are numerous chemical compounds that exhibit inhibitive properties. Of these, however, only inorganic corrosion inhibitors have been commercially used for corrosion inhibition in a high density SFRMs. Calcium nitrite has been used with Monokote® Z-156T from W. R. Grace. Monolote Z-156T is a high density (>50 lbs/ft3) cementitious fireproofing material for tunnels and severe environmental exposure.
Yet, organic corrosion inhibitors have not traditionally been used in SFRMs, in part due to the SFRM's alkaline nature, and in part due to the of lack of guidance and uncertainty in the industry. Although both SFRM and concrete contain significant amounts of Portland cement, the two classes of product commonly show different properties with respect to additives. Corrosion inhibitors used in concrete are not indicated for SFRMs due to the differences in application, requirements and different effects of common additives. Concrete is normally applied by precasting or casting in place. SFRMs are normally applied by spraying onto structural steel members through a hose under 30-80 psi air pressure. To be effective the SFRM requires good pumpability, good hangability and strong adhesion on the substrate.
Moreover, the effect of different additives in both concrete and SFRMs are not similar. For example, the addition of a superplasticizer in concrete allows for the use of less water and increases the concrete's physical strength. The use of a superplasticizer in a SFRM results in a decrease in the SFRM's physical strength. Similarly, the use of a shrinkage reducing agent reduces shrinkage in concrete but does not in a SFRM. The use of silica fume fillers in concrete produces increased physical strength. In a SFRM silica fume fillers also increase physical strength. But, they also significantly reduce set time (resulting in problems with pump-ability and spray-ability), reduce adhesion (to the point of delamination) and increase shrinkage (which can lead to cracking). Finally, the use of Class C fly ash in concrete reduces shrinkage and increases physical strength. In a SFRM, however, Class C fly ash increases shrinkage and reduces adhesion (to the point of delamination).
The present disclosure is directed to a spray applied fire resistant material having organic corrosion inhibitors, such as an aldonic acid or a salt thereof or a benzoic acid or a salt thereof, to reduce or eliminate corrosion of the SFRM coated substrate.